The present invention generally relates to a refrigerator, and more particularly, to reduction of noises produced during operation of the refrigerator.
Recently, most refrigerators are produced in a two-door type or three door type having, for example, a freezing chamber and refrigerating chamber, etc. so that the cooling temperature may be divided according to objects for use.
Commonly, as shown in FIG. 5, the refrigerator R of the above described type has a freezing chamber 1 to provide the lowest temperature at the uppermost portion thereof. The freezing chamber 1 has a door 12 pivotally provided at its front side for selective opening and closing of said chamber, while, at the back side of the freezing chamber 1, there is provided a blasting louver 5 formed with blasting holes 14 for sending out cooled air into the freezing chamber 1. Behind said blasting louver 5, a fan fixing plate 10 on which an axial flow fan 3 is fixed, is provided. Below the axial flow fan 3 referred to above, a heat exchanger 4 is disposed in a suction side space 7 defined between the fan fixing plate 10 and the inner wall surface of a rear panel 9 of the refrigerator R. Meanwhile, in the freezing chamber 1 in a bottom wall under the door 12, an opening 13 is formed to be communicated with the heat exchanger 4.
By the above arrangement, air in the above refrigerator R is adapted to be normally circulated by the axial flow fan 3 as indicated by arrows. Accordingly, the interior of the refrigerator R can be maintained at predetermined low temperatures as the air is cooled by the refrigerator 4 as it is circulated in the manner as described above.
Incidentally, the air referred to above is formed with turbulence in its flow when sent out by the axial flow fan 3 so as to be turbulent flow, because an air suck-in portion of the axial flow fan 3 is limited at the lower portion, with the blasting louver 5 being provided before the blasting portion. Thus, the air in the form of the turbulent flow as described above is producing the so-called turbulent noise having a wide range of frequency region.
The above turbulent noise tends to readily induce resonance, since the interior of the freezing chamber 1 and the suction side space 7 have a resonance frequency Fr represented by a following equation. EQU Fr=n.multidot.C/(2.multidot.L) (1)
wherein C is a speed of sound (m/s), L is a resonance dimension (m), and n is an integer (1,2 . . . ).
By the above fact, the suction side space 7 is to have a resonance frequency Fr determined by the resonance frequency L as shown in FIG. 6, and the resonance referred to above becomes a main factor which increases the noise during operation of the refrigerator.
Accordingly, as shown in FIG. 5, on the outer walls of the freezing chamber 1, layers of a sound absorbing material 6 are provided for preventing the noises generated inside the freezing chamber 1 and the suction side space 7, from leaking out of the refrigerator R. For the above sound absorbing material 6, a porous material, e.g. glass wool, felt or the like is employed, whereby the noises produced in the freezing chamber 1 and the suction side space 7 of the refrigerator R may be lowered.
However, in the conventional refrigerators as described so far, it is still difficult to sufficiently suppress the noises generated within the freezing chamber 1 and the suction side space 7, due to the fact that the above noises have a wide range of frequency regions, whereas the sound absorbing material commonly employed has a superior sound absorbing coefficient only above certain frequencies, e.g. 600 Hz. In other words, in the conventional refrigerators as described so far, since the frequency regions of the noises are not fully in agreement with the frequency regions of the sound absorbing material 6 for absorbing such noises, said noises tend to leak out of the refrigerator R.
Accordingly, in a refrigerator, if it is intended to fully reduce the noises generated within the freezing chamber 1 and the suction side space 7, it is necessary to largely increase the thickness of each layer of the sound absorbing material 6 or to use a sound absorbing material made of a special material superior in sound absorbing characteristics if it is thin in the thickness of its layer.
In the case where the thickness of the layer of the sound absorbing material is increased to a large extent, there is brought about such a problem that it becomes necessary to increase external dimensions of the refrigerator, or to reduce the volume of the freezing chamber 1. On the other hand, when the sound absorbing material of a special quality superior in the sound absorbing characteristics even if its layer is thin, is employed, another problem is involved such as cost increase of the refrigerator on the whole, since the sound absorbing material of the particular quality is generally expensive.